1. Field of the Invention
This invention relates to an ink jet droplet apparatus having a generator for charging ink droplets formed from a liquid stream by a sonic transducer for use in non-impact printing and more particularly to a phase correction system associated with the apparatus for optimally determining during a test period the phase time associated with the operation of the charging generator and the sonic transducer.
2. Prior Art
It is a characteristic of an ink jet droplet apparatus used for document printing that the point of break-off where the ink stream separates into droplets may temporally vary within any given time frame relative to the initialization of a sonic transducer which induces droplet break-off. This is a result of the acoustic characteristics of the ink, and in particular, the pressure of the ink stream as it is emitted from its jet source in the apparatus and the viscosity of the ink. The viscosity, in turn, is dependent upon the ink temperature, and the solvent content of the ink. These viscosity dependencies will vary through time and thus affect the temporal position of the break-off point relative to the sonic transducer at charging time. Since the plates for charging the droplets are spatially and temporally fixed relative to the sonic transducer, any temporal variance of the break-off point through time will cause suboptimal charging of the droplets. At relatively low printing speeds, such temporal variance could be tolerated within certain limits since printing precision would not be critically affected. Alternatively at a trade off in higher cost, variance in the viscosity dependencies could be lowered or eliminated by strictly controlling the ink environment. Where higher printing speeds are desired without resorting to a relatively high cost ink environment new solutions are then required to overcome the supra problems.